Process of wrapping articles in polyolefin material



Nov. 14, 1967 J. W. PANTENBURG PROCESS OF WRAPPING ARTICLES IN POLYOLEFIN MATERIAL,

Filed June 24, 1965' FIG-2 FIG I I N VENTOR. Jain/(d. 24A 7iA/502G FIGQS United States Patent 6 3,352,085 PROCESS OF WRAPPING ARTICLES IN POLYOLEFIN MATERIAL Joseph W. Pantenburg, San Leandro, Calif., assignor to Crown Zellerbach Corporation, San Francisco, Calif.,

a corporation of Nevada Filed June 24, 1965, Ser. No. 466,798 9 Claims. (Cl. 53-32) This invention relates to packaging of small articles. More particularly, the present invention relates to a process of wrapping individual small articles, such as candy, cough drops, bubble gum and other confectionary articles in a sheet of thin stretchable polyolefin material, particularly a polypropylene or polyethylene film, and to packages resulting therefrom.

Many packaging sheet materials have been used to wrap such articles automatically using twist wrapping machines which by means of gripping jaws twist the opposed ends of the wrapper to form a closed twisted neck at each end of the wrapped article.

The wrapping materials which either have been employed in packaging individual articles in such machines or described in the prior art include those which are characterized by very little elongation, such as waxed paper or cellophane, as well as the so called thermostretchable plastic sheet materials, such as rubber hydrochloride, polyvinyl chloride, polyvinyl acetate, ethylcellulose and the like. The latter materials require application of heat prior to stretching in order to impart suflicient elongation thereto. Upon warming such materials well above ambient room temperature to a point where they become readily stretchable and elastic, the twisting action may be effected readily and upon cooling the twist remains permanent and thus the article is wrapped permanently thus forming a package in which the article is tightly enclosed. While application of heat to the wrapper during the packaging operation may be satisfactory for certain articles, it would be objectionable in packaging confectionary articles, such as candy, inasmuch as such articles would be softened, melted, or otherwise degraded when exposed to an elevated temperature required to heat the wrapper or the gripping jaws adjacent thereto.

Attempts have been made to package small articles by means of twist wrapping machines using polyolefin films, such as polypropylene or polyethylene, which are stretchable at normal room temperature. However, due to inherent characteristics of such films, such attempts have been unsuccessful inasmuch as after twisting the open ends of the wrapper, the twisted ends have the tendency of unwinding shortly after the twisting operation and thus produce an unsatisfactorily packaged article which would be objectionable to prospective purchasers.

I have now discovered that the above mentioned packaging procedures employed in connection with twist wrapping machines can be improved and applied to stretchable polyolefin films to produce an attractive package having a permanently twisted closure at each end thereof.

It is, therefore, the principal object of the present invention to provide a process for wrapping small articles in a normally stretchable polyolefin film in such a manner as to produce a package having a permanently twisted end closure at each end thereof.

A further object of this invention is to provide an improved process for packaging confectionary articles in individual sheets of thin, stretchable polyolefin film, which process is rapid and economical, does not require any application of heat and produces neatly wrapped articles with two twisted projecting ends of the sheet.

Another object of this invention is to provide an attracice tive and sanitary package comprising a small article wrapped in a sheet of a thin, stretchable polyolefin film with a permanently twisted closure at each end of the package.

Other objects of this invention will be apparent to those skilled in the art from the following disclosures.

Generally stated, the herein described process of wrapping small individual articles comprises placing the article on a thin sheet of stretchable polyolefin film, encircling the article with the sheet in such a manner as to form a tube with open ends, clamping each of the two opposite free ends of the sheet encircled around the article by a pair of gripping jaws having on the work surface thereof a special, rough metallic coating, stretching and twisting the free ends of the sheet in the same direction beyond the yield point of the film but prior to its break point, to produce a wrapped article having a permanently twisted closure at each end thereof.

The present invention will be described in more detail with reference to the accompanying drawing, in which:

FIG. 1 is a perspective view of the sheet with the article to be wrapped placed thereon,

FIG. 2 is a perspective view of the article encircled with the sheet,

FIG. 3 is a sectional view of a pair of gripping jaws clamping the free ends of the sheet containing the article prior to twisting,

FIG. 4 illustrates the completely wrapped article with a twisted closure at each end thereof,

FIG. 5 is a detail plan view of a gripping jaw having a metallic coating on the work surface thereof, and

FIG. 6 is an enlarged fragmental sectional view of the gripping jaw taken on the line 66 of FIG. 5.'

The process of this invention may conveniently be carried out on conventional wrapping machines known in the trade as twist wrapping machines. Such machines comprise the combination of mechanism for enclosing individual articles, such as candy, tablets, chewing gum, or the like, in a sheet material and conveying the articles with the wrapping sheets folded about them in tubular form to the twisting station, in which is mounted a twisting mechanism including two pairs of rotary grippers provided with gripping jaws. The grippers are each provided with separate actuating and reciprocating mechanisms and are adapted to operate simultaneously on the ends of the wrapping sheet clamped by the gripping jaws. A machine very suitable in the practice of the present invention is described in the US. Patent No. 2,046,262. However, other similar twist wrapping machines also are suitable for wrapping articles by the process of this invention.

Although the opposed work surfaces of the jaws may be corrugated or provided with any suitable type of projections in order to improve their gripping action and thus reduce somewhat slippage of the clamped wrapper during the stretching and twisting operation, an important charactertisic of this invention lies in providing the entire work surface of each of the gripping jaws with a strongly adherent high-melting point abrasion-resistant rough metallic coating in order to prevent slippage, thereby insuring a positive gripping and twisting action of the jaws when thin polypropylene or polyethylene films are employed in the packaging process of this invention without application of any heat thereto.

A metallic coating which is particularly suitable in the practice of this invention is about 0.002-0.003 inch thick and comprises a major proportion of tungsten carbide. Such coating is applied to the surface of the jaws in such a manner as to impart thereto a roughness in the range of from about 200 to about 500 microinches R.M.S. (root mean square) and a high wear resistance. The preferred range of the roughness of the work surface of the jaws is in the range from about 250 to about 450 microinches R.M.S. A hard coating which is particularly well adapted for the wrapping operation according to this invention comprises from 90%-93% of tungsten carbide and from 7%10% of cobalt by weight.

In order to provide a metallic coating which will strongly adhere to the surface of the gripping jaws, fine metallic particles may be deposited on the jaws surface by means of a detonation gun using the procedure described in the US. Patent No. 2,714,563.

I have found that under continuous operating conditions of a twist wrapping machine provided with gripping jaws coated with a mixture of tungsten carbide and cobalt within the range mentioned hereinabove and having a thickness of the coating of about 0.003 of an inch, the coated gripping jaws performed very satisfactorily for a period of six months using cast polypropylene sheets of 1 mil thickness.

As pointed out hereinabove, the process of this invention is applicable to stretchable sheets of thin polyolefin films, particularly polypropylene and polyethylene. Among the various types of films which may be employed in the practice of the invention, the preferred types are those formed from unplasticized cast (unoriented) polypropylene and fromcast polypropylene containing up to about 1% by weight of a plasticizer. Medium and high density polyethylene, copolymers of propylene and ethylene and thin laminates of polypropylene and polyethylene also are suitable for use in the herein described process.

In contrast to other conventionally employed wrapping sheet materials such as waxed paper or cellophane, cast polypropylene and polyethylene films do not possess the so called dead fold characteristic. In other words, whereas such conventional sheet materials which have been used for packaging on twisting machines presented, after twisting action, permanently twisted ends, polypropylene and polyethylene films would unwind after twisting operation because of the lack of this dead fold characteristic. Other thermostretchable polymeric sheet materials, such as rubber hydrochloride, which have been previously suggested for packaging on twisting machines require application of heat to bring them to an elevated temperature at which they readily stretch and become sufficiently elastic to be subjected to a positive twisting action.

It should therefore be emphasized that, whereas the prior art wrapping processes are based on the use of sheet materials characterized either by very little elongation or those which acquire substantial elongation upon heating to an elevated temperature, the present process utilizing polyolefin films, such as polypropylene or polyethylene, is carried out at ambient room temperature, i.e. without application of heat to either the sheet material or the gripping jaws, and produces the desired permanently twisted closures at each end of the finished package.

According to the preferred practice of the present invention, as shown in the drawing, a confectionary article 12, such as candy, is placed on a square or rectangular sheet 10 of an unplasticized cast polypropylene film of 1 mil thickness, the sheet having previously been cut off from a roll of film mounted on a reel (not shown). The article 12 is then encircled by the sheet thus forming an open-ended tube around the long axis of the article, as shown in FIG. 2. Each of the two projecting free ends of the sheet is clamped by a pair of gripping jaws 14 having diagonally corrugated opposite working surfaces 14acoated with a strongly bonded thereto continuous metallic coating consisting of a mixture of 91% of tungsten carbide and 9% cobalt by weight. The thickness of the coating is 0.003 of an inch and the roughness of the coated surface is 350 microinches R.M.S. Both projecting ends of the sheet clamped by the jaws 14 are stretched and simultaneously twisted in the same direction, as illustrated in FIG. 3 beyond the yield point of the film but prior to its break point to complete the wrapping operation. During stretching the sheet to produce satisfactorily twisted end closures, a twist equivalent to 1.52 full rotations of the coated gripping jaws usually is sufficient to exceed the yield point of the 1 mil thick cast polypropylene film referred to hereinabove without attaining its break point. After the finished package 18 having two twisted rosette-like end closures 16 is formed, the clamped ends of the sheet are released from the gripping jaws which are free to receive another wrapping sheet and a candy for the subsequent twisting step.

The yield point and the break point of a plastic film, i.e. the point exceeding the tensile strength of a film at break, may conveniently be determined on an Instron stress-strain tester. Such physical properties of plastic sheets are well known in the art. The yield point is defined in the 1964 edition of A.S.T.M. Standards, part 27, appendix to D63861T, page 215.

From the above disclosure, it is apparent that the presently described process for wrapping small individual articles, such as confectionary articles, is highly satisfactory inasmuch as thin cast polyolefin films, i.e. polypropylene and polyethylene, which could not be employed heretofore are now potentially useful in producing economically attractive and sanitary packages having permanently twisted both end closures.

It is to be understood that changes and modifications may be made in regard to specific details of the invention herein described which are intended to be included within the scope of the appended claims.

I claim:

1. The process of wrapping an article which comprises placing the article on a thin sheet of stretchable polyolefin film, encircling the article with the sheet, clamping each of the two opposite ends of the sheet encircled around the article by a pair of gripping jaws having on the work surface thereof a strongly adherent, rough metallic coating comprising a major proportion of tungsten carbide, said surface being characterized by a roughness in the range of from about 200 to about 500 microinches R.M.S. and high wear resistance, stretching and simultaneously twisting the clamped ends of the sheet in the same direction beyond the yield point but prior to the break point of the polyolefin film, while maintaining the sheet at ambient room temperature, thereby producing a wrapped article having a permanently twisted closure at each end.

2. The process of claim 1 wherein the polyolefin film is cast polypropylene film.

3. The process of claim 1 wherein the polyolefin film is a cast polypropylene film having a thickness about 0.75-15 mils.

4. The process of claim 1 wherein the polyolefin film is a medium density polyethylene film.

5. The process of claim 1 wherein the polyolefin film is a high density polyethylene film.

6. The process of claim 1 wherein the metallic coating comprises %-93% of tungsten carbide and 7%10% of cobalt by weight.

7. The process of claim 1 wherein the roughness of the work surface is in the range of from about 250 to about 450 microinches R.M.S.

8. The process of claim 1 wherein the polyolefin film is cast polypropylene film and the clamped ends of the sheet are subjected to a twist of 1.52 full rotations of the gripping jaws.

9. The process of wrapping a confectionary article which comprises placing the article on a stretchable sheet of unplasticized cast polypropylene film having a thickness of 075-15 mil, encircling the article with the sheet, clamping each of the two opposite ends of the sheet encircled around the article by a pair of gripping jaws having corrugated work surface coated with a strongly adherent, rough metallic coating comprising 90%93% of tungsten carbide and 7%-10% of cobalt by weight, said work surface being characterized by a roughness in the range of from about 250 to about 450 microinches R.MiS. and high wear resistance, stretching and simultaneously subjecting the clamped ends of the sheet to a twisting action of the gripping jaws in the same direction beyond the yield point but prior to the break point of the film, while maintaining the jaws and the sheet at ambient room temperature during the stretching and twisting thereof, and releasing the sheet from the jaws, thereby producing a polypropylene-wrapped confectionary article having a permanently twisted closure at each end of the sheet.

References Cited UNITED STATES PATENTS Kemp 22987 X Nydegger 22987 Rumsey 53-370 Walton 53-112 Rumsey 53-370 Thatcher 53--370 Enoch 229-87 X TRAVIS S. MCGEHEE, Primary Examiner.

N. ABRAMS, Assistant Examiner. 

1. A PROCESS OF WRAPPING AN ARTICLE WHICH COMPRISES PLACING THE ARTICLE ON A THIN SHEET OF STRETCHABLE POLYOLEFIN FILM, ENCIRCLING THE ARTICLE WITH THE SHEET, CLAMPING EACH OF THE TWO OPPOSITE ENDS OF THE SHEET ENCIRCLED AROUND THE ARTICLE BY A PAIR OF GRIPPING JAWS HAVING ON THE WORK SURFACE THEREOF A STRONGLY ADHERENT, ROUGH METALLIC COATING COMPRISING A MAJOR PROPORTION OF TUNGSTEN CARBIDE, SAID SURFACE BEING CHARACTERIZED BY A ROUGHNESS IN THE RANGE OF FROM ABOUT 200 TO ABOUT 500 MICROINCHES R.M.S. AND HIGH WEAR RESISTANCE, STRETCHING AND SIMULTANEOUSLY TWISTING THE CLAMPED ENDS OF THE SHEET IN THE SAME DIRECTION BEYOND THE YIELD POINT BUT PRIOR TO THE BREAK POINT OF THE POLYOLEFIN FILM, WHILE MAINTAINING THE SHEET AT AMBIENT ROOM TEMPERATURE, THERBY PRODUCING A WRAPPED ARTICLE HAVING A PERMANENTLY TWISTED CLOSURE AT EACH END. 